Tool path preparing method and machining method

ABSTRACT

The movement position of the roughing tool is calculated, in S 109 , by adding the finishing allowance to the movement position of the finishing tool so that the path of the roughing tool is shifted in the direction perpendicular to the rotation center axis of the main spindle rotation motor from the path of the finishing tool by the finishing allowance. Then, a gap between the movement position of the roughing tool in the direction of the rotation center axis of the main spindle rotation motor and the workpiece W is calculated, and when the gap is not larger than a predetermined value G, in S 113,  the movement position of the roughing tool is corrected in the direction perpendicular to the rotation center axis of the main spindle rotation motor so that the roughing tool does not cut in the inside of the finishing portion of the workpiece. The movement position of the roughing tool is corrected so that the movement speed of the roughing tool in the direction perpendicular to the rotation center axis of the main spindle rotation motor is a predetermined value.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a tool path preparing method forpreparing a tool path to simultaneously conduct a roughing and finishingoperations, and to a machining method employing the tool path preparingmethod.

[0003] 2. Description of the Related Art JP-A-63-200943 discloses a toolpath preparing method and a machining method employing the tool pathpreparing method, for example. According to JP-A-63-200943, controllinga position of a finishing tool automatically controls another tool tooperate simultaneously at a rough-cut position having a smaller depth ofcut by an arbitrarily given finishing allowance. In other words, onlythe position of the tip of the finishing tool is programmed, and theroughing tool is automatically controlled at a rough cut positionleaving only the finishing allowance.

[0004] However, there are the following problems in the tool pathpreparing method and machining method as disclosed in JP-A-63-200943.

[0005] If the path of the roughing tool is prepared by shifting thefinishing tool in the direction of the main spindle by an offsetdistance between the roughing tool and the finishing tool, and furthershifting it in the direction perpendicular to the main spindle by thefinishing allowance, a cutting which includes the shape perpendicular toor approximately perpendicular to the main spindle (for example, astepped portion) would be impossible, because the roughing operationcuts in to the inside of the finishing portion.

[0006] In order to prevent the cut-in by the roughing tool, it isnecessary that a feed of the finishing tool is stopped, and the roughingtool is retreated to a position at which the cut-in is not caused,whichresults in along machining time. Further,because the feed of thefinishing tool is stopped, a scar (cutter mark) is generated on theworkpiece at a position the finishing tool is stopped.

SUMMARY OF THE INVENTION

[0007] In view of the foregoing problems, an object of the presentinvention is to provide a tool path preparing method and a machiningmethod employing the tool path preparing method by which the machiningtime of the workpiece by the roughing tool and the finishing tool isreduced, and the scar on the surface of the workpiece can be suppressed.

[0008] According to the present invention, there is provided a method ofpreparing a tool path to simultaneously conduct a roughing and afinishing operations by moving at least one of a workpiece to be rotatedaround a predetermined axis and tools including a roughing tool and afinishing tool off set-arranged in the axial direction of thepredetermined axis, the method comprising:

[0009] calculating a path of the roughing tool based on a path of thefinishing tool by shifting the path of the finishing tool by a finishingallowance in the direction perpendicular to the predetermined axis; and

[0010] correcting the calculated path of the roughing tool so as to forma predetermined gap between the workpiece and the roughing tool in theaxial direction of the predetermined axis.

[0011] In the tool path preparing method according to the presentinvention, after shifting the path of the finishing tool by a finishingallowance in the direction perpendicular to the predetermined axis tocalculate the path of the rouging tool, the calculated path of theroughing tool is corrected so that a predetermined gap is formed betweenthe workpiece and the roughing tool when viewed in the axis direction ofthe predetermined axis, therefore, the cut-in into the inside of thefinishing portion by the roughing tool can be prevented without stoppingthe feed of the finishing tool. As the result, the machining time of theworkpiece by the roughing tool and the finishing tool can be reduced.Further, because the feed of the finishing tool is not stopped, it canbe suppressed that the cutter mark is formed on the surface of theworkpiece by the finishing tool.

[0012] It is preferable that the path of the roughing tool is correctedso that the moving speed of the roughing tool in the directionperpendicular to the predetermined axis is a predetermined value. Insuch the manner, when the path of the roughing tool is corrected, bycorrecting the path of the roughing tool so that the movement speed ofthe roughing tool in the direction perpendicular to a predetermined axisis a predetermined value, the roughing tool can be smoothly moved, andthe cutting load by the roughing tool can be decreased, and thevariation of the cutting load can be suppressed.

[0013] It is preferable that the path of the roughing tool is correctedso that the roughing tool moves at a predetermined acceleration from aposition, at which the gap between the workpiece and the roughing toolin the axis direction of the predetermined axis becomes a predeterminedvalue, in the direction perpendicular to the predetermined axis. In thismanner, when the path of the roughing tool is corrected, by correctingthe path of the roughing tool so that the roughing tool is moved at apredetermined acceleration in the direction perpendicular to apredetermined axis from a position at which a gap between the workpieceand the roughing tool in the axis direction of the predetermined axisbecomes a predetermined value, the path of the roughing tool can beeasily corrected. Further, the variation of the cutting load by theroughing tool can be more suppressed.

[0014] According to the present invention, there is provided a method ofmachining a workpiece to be rotated around a predetermined axis,comprising:

[0015] arranging tools including a roughing tool and a finishing tooloffset in the axial direction of the predetermined axis;

[0016] calculating a path of the roughing tool based on a path of thefinishing tool by shifting the path of the finishing tool by a finishingallowance in the direction perpendicular to the predetermined axis;

[0017] correcting the calculated path of the roughing tool so as to forma predetermined gap between the workpiece and the roughing tool in theaxial direction of the predetermined axis; and

[0018] moving at least one of the workpiece and the tools, therebysimultaneously conducting a roughing and a finishing operations.

[0019] Because, in the processing method according to the presentinvention, according to the tool path prepared by the tool pathpreparing method described in the first to the third aspects of thepresent invention, because the roughing and the finishing operations aresimultaneously conducted by the roughing tool and the finishing tool,the cut-in into the inside of the finishing portion by the roughing toolcan be prevented without stopping the feed of the finishing tool. As theresult, the machining time of the workpiece by the roughing tool and thefinishing tool can be reduced. Further, because the feed of thefinishing tool is not stopped, it can be suppressed that the cutter markis formed on the surface of the workpiece by the finishing tool.

[0020] Typically, the tool path can be prepared by a method comprisingthe steps of:

[0021] reading initial positions of a roughing tool and a finishingtool;

[0022] initializing the number of cumulative rotations of a workpiece tobe rotated around a predetermined axis;

[0023] reading a position data calculation program;

[0024] settling a movement position of the finishing tool at apredetermined number of cumulative rotations of the workpiece;

[0025] calculating a movement position of the roughing tool at thepredetermined number of cumulative rotations of the workpiece;

[0026] correcting the calculated movement position of the roughing toolin a direction perpendicular to and away from the predetermined axiswhen a gap between the roughing tool and the workpiece in the axialdirection of the predetermined axis is not larger than a predeterminedvalue; and

[0027] storing the movement position of the roughing tool and thefinishing tool in a position data table memory.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a block diagram showing the structure of a machine toolaccording to an embodiment of the present invention.

[0029]FIG. 2A is a view showing the shape of the workpiece before theprocessing, and FIG. 2B is a view showing the shape of the processedworkpiece, both for explaining an example of a processing operation of aworkpiece in the machine tool according to the embodiment of the presentinvention.

[0030]FIG. 3 is a flow chart for explaining a determination processingoperation of movement positions of the roughing tool and the finishingtool.

[0031]FIG. 4 is a flow chart for explaining an output processingoperation of the roughing tool position command signal and the finishingtool position command signal in the machine tool according to theembodiment of the present invention.

[0032]FIG. 5 is a diagram showing the path of the roughing tool and thepath of the finishing tool in the machine tool according to theembodiment of the present invention.

[0033]FIG. 6 is a diagram showing the path of the roughing tool and thepath of the finishing tool in the machine tool according to theembodiment of the present invention.

[0034]FIG. 7A is a diagram showing the change of the movementacceleration of the roughing tool, and FIG. 7B is a diagram showing thechange of the movement speed of the roughing tool, both for explainingthe operation of the roughing tool in the machine tool according to theembodiment of the present invention

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0035] Preferred embodiments of a tool path preparing method and amachining method will be described in detail below according to thepresent invention, with reference to the accompanying drawings. In thisconnection with the description on the drawings, the same parts as thoseof the conventional one are denoted by assigning the same referencenumerals, and the duplication of the explanation will be omitted. In thepresent embodiments, an example in which the present invention isapplied to a machine tool, and particularly, to a Swiss type machinetool, will be shown.

[0036]FIG. 1 is a block diagram showing the structure of a machine toolaccording to an embodiment of the present invention. In FIG. 1, amachine tool 1 has a main spindle rotation motor 11, roughing toolmovement motor 21, finishing tool movement motor 31, workpiece movementmotor 41, and control unit section 51 for controlling the drive of eachof the motors 11, 21, 31, and 41.

[0037] The main spindle rotation motor 11 is a motor for rotating a mainspindle (not shown) structured so that the workpiece can be held, and isconnected to the control circuit section 51 through a driving circuit 12and a main spindle rotation control circuit 13. Further, a pulsegenerator 14 for detecting the rotation of the main spindle rotationmotor 11 is provided on the main spindle rotation motor 11. The outputof the pulse generator 14 is connected to the control unit section 51and a speed signal generation circuit 15, and the rotation detectionsignal outputted from the pulse generator 14 is inputted into thecontrol unit section 51 and the speed signal generation circuit 15. Thepulse generator 14 generates the rotation detection signal beingsynchronized with the rotation of the main spindle rotation motor 11(main spindle), and outputs to the control unit section 51 and speedsignal generation circuit 15. Herein, the rotation center axis of themain spindle rotation motor 11 (main spindle) constitutes an axisextending to a predetermined direction.

[0038] The speed signal generation circuit 15 converts the rotationdetection signal outputted from the pulse generator 14 into the mainspindle rotation speed signal which represents the rotation speed of themain spindle rotation motor 11 (main spindle). The output of the speedsignal generation circuit 15 is connected to the main spindle rotationcontrol circuit 13, and the converted main spindle rotation speed signalis inputted into the main spindle rotation control circuit 13.

[0039] The main spindle rotation control circuit 13 compares the mainspindle rotation speed command signal outputted from the control unitsection 51 which will be described later, to the main spindle rotationspeed signal outputted from the main spindle rotation control circuit13, and generates the control signal corresponding to the differencetherebetween. The control signal generated by the main spindle rotationcontrol circuit 13 is outputted to the driving circuit 12.

[0040] The driving circuit 12 controls electric power supply to the mainspindle rotation motor 11 so that the rotation speed of the main spindlerotation motor 11 (main spindle) is the main spindle rotation speedcommand value, which will be described later, according to the controlsignal outputted from the main spindle rotation control circuit 13.These driving circuit 12,main spindle rotation control circuit 13, andspeed signal generation circuit 15 constitute the feed back controlsystem of the rotation speed of the main spindle rotation motor 11 (mainspindle).

[0041] The roughing tool movement motor 21 is a motor to move theroughing tool to rough-cut the workpiece, for example, in the direction(X₁ axis direction) perpendicular to the rotation center axis of themain spindle rotation motor 11 (main spindle), and is connected to thecontrol unit section 51 through a driving circuit 22 and a roughing toolfeed control circuit 23. Further, to the roughing tool movement motor21, a pulse generator 24 is provided to detect the rotation of theroughing tool movement motor 21. The output of the pulse generator 24 isconnected to the roughing tool feed control circuit 23, and the rotationdetection signal of the pulse generator 24 is inputted into the roughingtool feed control circuit 23. The pulse generator 24 generates therotation position signal at each predetermined rotation angle of theroughing tool movement motor 21, and outputs it to the roughing toolfeed control circuit 23.

[0042] The roughing tool feed control circuit 23 recognizes the actualmovement position of the roughing tool according to the rotationposition signal outputted from the pulse generator 24, and compares themovement position of the recognized actual roughing tool to the roughingtool position command signal outputted from the control unit section 51which will be described later, and according to the comparison result,generates the roughing tool drive signal. The roughing tool drive signalgenerated in the roughing tool feed control circuit 23 is outputted tothe driving circuit 22. The driving circuit 22 controls the electricpower supply to the roughing tool movement motor 21 according to theroughing tool drive signal outputted from the roughing tool feed controlcircuit 23. These driving circuit 22 and the roughing tool feed controlcircuit 23 constitute the feed back control system of the movementposition of the roughing tool.

[0043] The finishing tool movement motor 31 is a motor to move thefinishing tool to finish-cut the workpiece, for example, in thedirection (X₂ axis direction) perpendicular to the rotation center axisof the main spindle rotation motor 11 (main spindle), and is connectedto the control unit section 51 through a driving circuit 32 and afinishing tool feed control circuit 33. Further, to the finishing toolmovement motor 31, a pulse generator 34 is provided to detect therotation of the finishing tool movement motor 31. The output of thepulse generator 34 is connected to the finishing tool feed controlcircuit 33, and the rotation detection signal of the pulse generator 34is inputted into the finishing tool feed control circuit 33. The pulsegenerator 34 generates the rotation position signal at eachpredetermined rotation angle of the finishing tool movement motor 31,and outputs it to the finishing tool feed control circuit 33.

[0044] The finishing tool feed control circuit 33 recognizes the actualmovement position of the finishing tool according to the rotationposition signal outputted from the pulse generator 34, and compares themovement position of the recognized actual finishing tool to thefinishing tool position command signal outputted from the control unitsection 51 which will be described later, and according to thecomparison result, generates the finishing tool drive signal. Thefinishing tool drive signal generated in the finishing tool feed controlcircuit 33 is outputted to the driving circuit 32. The driving circuit32 controls the electric power supply to the finishing tool movementmotor 31 according to the finishing tool drive signal outputted from thefinishing tool feed control circuit 33. These driving circuit 32 and thefinishing tool feed control circuit 33 constitute the feedback controlsystem of the movement position of the finishing tool.

[0045] The work piece movement motor 41 is a motor to move theworkpiece, for example, in the direction (Z axis direction) in parallelwith the rotation center axis of the main spindle rotation motor 11(main spindle), and is connected to the control unit section 51 througha driving circuit 42 and a workpiece feed control circuit 43. Further,to the workpiece movement motor 41, a pulse generator 44 is provided todetect the rotation of the workpiece movement motor 41. The output ofthe pulse generator 44 is connected to the workpiece feed controlcircuit 43, and the rotation detection signal of the pulse generator 44is inputted into the workpiece feed control circuit 43. The pulsegenerator 44 generates the rotation detection signal at eachpredetermined rotation angle of the workpiece movement motor 41, andoutputs it to the workpiece feed control circuit 43.

[0046] The workpiece feed control circuit 43 recognizes the actualmovement position of the workpiece according to the rotation detectionsignal outputted from the pulse generator 44, and compares the movementposition of the recognized actual workpiece to the workpiece positioncommand signal outputted from the control unit section 51 which will bedescribed later, and according to the comparison result, generates theworkpiece drive signal. The workpiece drive signal generated in theworkpiece feed control circuit 43 is outputted to the driving circuit42. The driving circuit 42 controls the electric power supply to theworkpiece movement motor 41 according to the workpiece drive signaloutputted from the workpiece feed control circuit 43. These drivingcircuit 42 and the workpiece feed control circuit 43 constitute the feedback control system of the movement position of the workpiece.

[0047]FIG. 2A is a view for explaining an example of the roughing andfinishing operations of the workpiece W in the machine tool 1, and theshape of workpiece W to be machined is shown. The bar like workpiece Wis, as shown in FIG. 2A, rotated around the rotation center axis 1 (inthe arrowed direction A in FIG. 2A) of the main spindle rotation motor11 (main spindle) by the main spindle rotation motor 11, and is moved inthe direction in parallel with the rotation center axis 1 (in thearrowed direction C in FIG. 2A) of the main spindle rotation motor 11 bythe workpiece movement motor 41.

[0048] The roughing tool 2 is moved in the direction (in the arroweddirection B, in FIG. 2A) perpendicular to the rotation center axis 1 ofthe main spindle rotation motor 11 by the roughing tool movement motor21, and the workpiece W is roughly cut into a desired shape. Thefinishing tool 3 is moved in the direction (in the arrowed direction B₂in FIG. 2A) perpendicular to the rotation center axis 1 of the mainspindle rotation motor 11 by the finishing tool movement motor 31, andthe workpiece W is finish-cut into a desired shape.

[0049] The roughing tool 2 and the finishing tool 3 are, as shown inFIG. 2A, arranged being offset by a predetermined distance (offsetamount) D, viewed in the direction in which the rotation center axis 1of the main spindle rotation motor 11 (main spindle) extends. Further,the roughing tool 2 and the finishing tool 3 are arranged at both sidesof the rotation center axis 1 of the main spindle rotation motor 11(main spindle) by sandwiching the axis between them, and the movementdirection of the roughing tool 2 and the movement direction of thefinishing tool 3 are set to be opposite to or cross each other.

[0050] In the present embodiment, as shown in FIG. 2B, the roughing andthe finishing operations are conducted from each side of the workpiece Wso that a stepped portion Wa having a surface almost perpendicular tothe rotation center axis 1 of the main spindle rotation motor 11 (mainspindle) may be formed on a portion of the bar-like workpiece W. By themovement of the workpiece W in the direction in parallel with therotation center axis 1 of the main spindle rotation motor 11, theroughing and the finishing operations are simultaneously conducted,however, because the roughing tool 2 and the finishing tool 3 arearranged being offset, the roughing operation is conducted preceding tothe finishing operation, on the workpiece W. In this connection, in FIG.2A, the arrowed B₁ direction is the X₁ axis direction, the arrowed B₂direction is the X₂ axis direction, and the arrowed C direction is the Zaxis direction.

[0051] The control unit section 51, as shown in FIG. 1, has a centralprocessing unit 52, count section 53, ROM 56, and RAM 57. The centralprocessing unit 52 is an operation section to conduct the signalprocessing of the whole of the control unit section 51. The countsection 53 is connected to the pulse generator 14, and is structured insuch a manner that the pulse signal outputted from the pulse generator14 is inputted through the interface, and the number of occurrences ofthe inputted pulse signals is counted. Further, the count section 53 isalso connected to the central processing unit 52, and is also structuredin such a manner that the counted number of occurrences of the rotationdetection signals inputted from the pulse generator 14, is outputted tothe central processing unit 52.

[0052] The ROM 56 is a memory section to store various processingprograms, including a position data calculation program. The positiondata calculation program is a calculation program to define the movementposition of the roughing tool 2 and the movement position of thefinishing tool 3 at each predetermined number of cumulative rotationsθ_(n) of the main spindle rotation motor 11 (main spindle).

[0053] The RAM 57 is structured in such a manner that the result ofvarious operations in the central processing unit 52 is temporarilystored so that it can be read out, and the position data table memory 57a is also stored. The position data table memory 57 a is structured insuch a manner that the movement position of the roughing tool 2 and themovement position of the finishing tool 3 at each predetermined numberof cumulative rotations θ_(n) of the main spindle rotation motor 11(main spindle) defined by the position data calculation program arerespectively stored as the position data of the roughing tool 2 and theposition data of the finishing tool 3. Herein, the position data(movement position) of the roughing tool 2 shows the path of theroughing tool 2, and the position data (movement position) of thefinishing tool 3 shows the path of the finishing tool 3.

[0054] The machining data input section 61 is, as shown in FIG. 1, asection in which various data relating to the machining of the workpieceW such as shape data and machining conditions are inputted, and the datainputted into the machining data input section 61 are sent to thecentral processing unit 52. The shape data include the finishingdimension, and the processing conditions include the accuracy and thematerial of the workpiece W, and the data relating to the machining modesuch as the roughing or finishing operation.

[0055] Further, the central processing unit 52 calculates theaccumulated number of cumulative rotation of the main spindle rotationmotor 11 (main spindle) according to the count result by the countsection 53 of the number of occurrences of the rotation detectionsignals inputted from the pulse generator 14.

[0056] Next, according to FIG. 3, the process operation to define themovement position of the roughing tool 2 and the movement position ofthe finishing tool 3 in the central processing unit 52 (control unitsection 51) will be described.

[0057] Initially, in S101, the central processing unit 52 reads theinitial positions of the roughing tool 2 and the finishing tool 3. InNext S103, the initial setting (θ=θ₀) of the number of cumulativerotations θ is conducted, and the sequence advances to S105. In S105,the central processing unit 52 reads the position data calculationprogram from the ROM 56. In the next S107, by using the position datacalculation program, according to the shape data and the machiningconditions inputted in the processing data input section 61, the centralprocessing unit 52 calculates and defines the movement position (themovement position in the X₂ direction) of the finishing tool 3 in thepredetermined number of cumulative rotations θ_(n) of the main spindlerotation motor 11 (main spindle), and advances to S109.

[0058] In S109, by using the position data calculation program,according to the movement position of the finishing tool 3 defined inS107, the central processing unit 52 calculates the movement position(the movement position in the X₁ direction) of the roughing tool 2 inthe predetermined number of cumulative rotations θ_(n) of the mainspindle rotation motor 11 (main spindle). In the calculation of themovement position of the roughing tool 2, the offset amount D of theroughing tool 2 and the finishing tool 3, and finishing allowance f areconsidered. The movement position of the roughing tool 2 is calculatedby adding the finishing allowance f to the movement position of thefinishing tool 3 so that the path of the roughing tool 2 is shifted inthe direction perpendicular to the rotation center axis 1 of the mainspindle rotation motor 11 by the finishing allowance f from the path ofthe finishing tool 3.

[0059] In next S111, a gap between the movement position of the roughingtool 2 calculated in S109 in the direction of the rotation center axis 1of the main spindle rotation motor 11 and the workpiece W is calculated,and it is determined whether this gap is not larger than a predeterminedvalue G. When the gap between the movement position of the roughing tool2 in the direction of the rotation center axis 1 of the main spindlerotation motor 11 and the workpiece W is not larger than thepredetermined value G (in S111, (Yes)), the sequence advances to S113.On the one hand, when it is larger than the predetermined value (inS111, (No)), the sequence advances to S115. The predetermined value G isset according to the feed speed of the workpiece W, the height of thestepped portion Wa of the workpiece W, the movable speed of the roughingtool 2, and finishing allowance f.

[0060] In S113, the movement position of the roughing tool 2 iscorrected and defined in the direction (X₁ direction) perpendicular tothe rotation center axis 1 of the main spindle rotation motor 11 so thatthe roughing tool 2 does not cut in the inside of the finishing portionof the workpiece W. Herein, the movement position of the roughing tool 2is corrected so that the movement speed of the roughing tool 2 in thedirection perpendicular to the rotation center axis 1 of the mainspindle rotation motor 11 is a predetermined value.

[0061] In next S115, the movement position of the finishing tool 3defined in S107, and the movement position of the roughing tool 2defined in S113 are stored in the position data table memory 57 a of theRAM 57 as the position data of the roughing tool 2 and the position dataof the finishing tool 3 corresponding to a predetermined number ofcumulative rotations θ_(n). After that, the sequence advances to S117,and according to the number of cumulative rotations of the main spindlerotation motor 11 (main spindle), it is determined whether the finishingtool 3 reaches the end portion (final position) of the finishing area ofthe workpiece W. When the finishing tool 3 reaches the end portion(final position) of the finishing area of the workpiece W (in S117,(Yes)), the processing ends.

[0062] On the one hand, when the finishing tool 3 does not reach the endportion (final position) of the finishing area of the workpiece W (inS117, (No)), the number of cumulative rotations θ_(n) of the workpiece Wis changed to θ_(n+1) in S119, and the sequence returns to S107, and themovement position of the finishing tool 3 in the predetermined number ofcumulative rotations θ_(n) of a new workpiece W is defined, and theprocessing is continued,

[0063] Next, according to FIG. 4, the output operation of the roughingtool position command signal and the finishing tool position commandsignal in the central processing unit 52 (control unit section 51) willbe described.

[0064] The central processing unit 52 determines, initially in S301,whether the finishing start command is outputted. When the finishingstart command is outputted (in S301, (Yes)), the sequence advances toS303. When the finishing start command is not outputted (in S301, (No)),the sequence returns and is ready for until the finishing start commandis outputted.

[0065] When the sequence advances to S303, the central processing unit52 reads the position data of the roughing tool 2 and the position dataof the finishing tool 3 stored in the position data table memory 57 a ofthe RAM 47. When the position data of the roughing tool 2 and theposition data of the finishing tool 3 are read, the sequence advances toS305, and the central processing unit 52 outputs the position data ofthe roughing tool 2 showing the movement position of the roughing tool 2as the roughing tool position command signal to the roughing tool feedcontrol circuit 23, and the position data of the finishing tool 3showing the movement position of the finishing tool 3 as the finishingtool position command signal to the finishing tool feed control circuit33. The roughing tool position command signal and the finishing toolposition command signal are outputted according to the count result inthe count section 53. In details, according to the count result in thecount section 53, every time when a predetermined number of cumulativerotations of the main spindle rotation motor 11 (main spindle) reachesthe predetermined number of cumulative rotations θ_(n) set in theposition data table memory 57 a, the corresponding rouging tool positioncommand signal and the finishing tool position command signal areoutputted.

[0066] After that, in S307, it is determined whether the rouging toolposition command signal and the finishing tool position command signalcorresponding to the final position data among the position data of theroughing tool 2 and the finishing tool 3 are outputted. When the rougingtool position command signal and the finishing tool position commandsignal corresponding to the final position data are not outputted (inS307, (No)), the sequence returns to S305, and every time when thenumber of cumulative rotations of the main spindle rotation motor 11(main spindle) reaches the predetermined number of cumulative rotationsθ_(n), the rouging tool position command signal and the finishing toolposition command signal are successively outputted, thereby, theroughing and finishing operations are simultaneously done on theworkpiece W. When the rouging tool position command signal and thefinishing tool position command signal corresponding to the finalposition data are outputted (in S307, (Yes)), the processing operationends.

[0067] The central processing unit 52 (control unit section 51) definesthe main spindle rotation speed command value appropriate for theroughing and the finishing operations, and outputs the defined mainspindle rotation speed command value as the main spindle rotation speedcommand signal to the main spindle rotation control circuit 13. The mainspindle rotation control circuit 13 outputs the control signal to thedriving circuit 12 according to the main spindle rotation speed commandsignal inputted from the central processing unit 52 so that the rotationspeed of the main spindle rotation motor 11 (main spindle) is apredetermined rotation speed. Further, the central processing unit 52(control unit section 51) defines the movement position of the workpieceW appropriate for the roughing and finishing operations (the positiondata of the workpiece W), and outputs the movement position of theworkpiece W as the workpiece position command signal to the workpiecefeed control circuit 43. The workpiece position feed control circuit 43outputs the control signal to the driving circuit 42 according to theworkpiece position command signal inputted from the central processingunit 52.

[0068] Next, by using FIG. 5, the path of the roughing tool 2 and thepath of the finishing tool 3 according to the movement position of theroughing tool 2 and the movement position of the finishing tool 3defined in the central processing unit 52 (control unit section 51),will be described. In this connection, in FIG. 5, for the explanation,the drawing is shown as a condition in which the X₁ direction and the X₂direction are in the same direction, and the path of the roughing tool 2and the path of the finishing tool 3 are overlapped with each other.

[0069] As shown in FIG. 5, the path F of the finishing tool 3 to theworkpiece W is prepared so that it overlaps with the outside shape ofthe workpiece W. In FIG. 5, F₁-F₁₂ show the movement positions of thefinishing tool 3 at every predetermined number of cumulative rotationsof the main spindle rotation motor 11 (main spindle).

[0070] The path R of the roughing tool 2 to the workpiece W is prepared,as shown in FIG. 5, in such a manner that it is shifted by the finishingallowance f from the path F of the finishing tool 3, viewed in thedirection perpendicular to the rotation center axis 1 of the mainspindle rotation motor 11. In FIG. 5, R1-R12 show the movement positionsof the roughing tool 2 at every predetermined number of cumulativerotations of the main spindle rotation motor 11 (main spindle), and thesame subscript in the drawing shows the same number of cumulativerotations, for example, the movement position F₁ of the finishing tool 3and the movement position R₁ of the roughing tool 2 show the movementposition at the same number of cumulative rotations. Further, themovement position of the roughing tool 2 and the movement position ofthe finishing tool 3 of the same subscript are shifted by the offsetamount D between the roughing tool 2 and the finishing tool 3, viewed inthe direction of the rotation center axis 1 of the main spindle rotationmotor 11.

[0071] From the movement position R₃ of the roughing tool 2 to themovement position R₅ of the roughing tool 2, because a gap between themovement position of the roughing tool 2 in the direction of therotation center axis 1 of the main spindle rotation motor 11 and theworkpiece W is not larger than a predetermined value, the movementposition of the roughing tool 2 is corrected so that it is moved in thedirection perpendicular to the rotation center axis 1 of the mainspindle rotation motor 11, as the workpiece W is moved (fed) in thedirection of rotation center axis 1 of the main spindle rotation motor11. The movement position of the roughing tool 2 is corrected so thatthe movement speed of the roughing tool 2 in the direction perpendicularto the rotation center axis 1 of the main spindle rotation motor 11 is apredetermined value.

[0072] Thereby, the path R of the roughing tool 2 to the workpiece W isprepared in such a manner that the movement position of the roughingtool 2 and the movement position of the finishing tool 3 of the samesubscript are shifted by the amount more than the finishing allowance f,viewed in the direction perpendicular to the rotation center axis 1 ofthe main spindle rotation motor 11, between the movement position R₃ andthe movement position R₅ of the roughing tool 2. As the result, apredetermined gap is formed between the workpiece in the direction ofthe rotation center axis 1 of the main spindle rotation motor 11 and theroughing tool 2, and the roughing tool 2 does not cut in the inside ofthe finishing portion of the workpiece W. In this connection, theshifting amount between the movement position of the roughing tool 2 andthe movement position of the finishing tool 3 while the movementposition of the roughing tool 2 is corrected, viewed in the direction ofthe rotation center axis 1 of the main spindle rotation motor 11,becomes the offset value D between the roughing tool 2 and the finishingtool 3, and does not change.

[0073] At the movement position F₆of the finishing tool 3 (the movementposition R₆ of the roughing tool 2), the finishing tool 3 reaches thestepped portion Wa of the workpiece W. At the movement position F₆ ofthe finishing tool 3, the movement (feed) of the workpiece W in thedirection of the rotation center axis 1 of the main spindle rotationmotor 11 is stopped. When the feed of the workpiece W is stopped, thefinishing tool 3 is moved to the movement position F7 of the finishingtool 3 in the direction perpendicular to the rotation center axis 1 ofthe main spindle rotation motor 11. At this time, the roughing tool 2 isnot moved, and stops at the movement position R₆ of the roughing tool 2.When the roughing tool 2 stops at the movement position R₆, the cuttermark by the roughing tool 2 is formed on the surface of the workpiece W,however, because this portion is cut off by the finishing tool 3, thecutter mark by the roughing tool 2 does not remain on the surface of thefinished workpiece W.

[0074] When the finishing tool 3 reaches the movement position F₇, themovement (feed) of the work piece W in the direction of the rotationcenter axis 1 of the main spindle rotation motor 11 starts, thereby, theroughing tool 2 and the finishing tool 3 are relatively moved to theworkpiece W in the direction of the rotation center axis 1 of the mainspindle rotation motor 11.

[0075] In this manner, according to the present embodiment, the movementposition of the roughing tool 2 is calculated so that it maybe shiftedwith respect to the finishing tool 3 by the finishing allowance f in thedirection perpendicular to the rotation center axis 1 of the mainspindle rotation motor 11, and then it is corrected so that apredetermined gap is formed between the workpiece W and the roughingtool 2, viewed in the direction of the rotation center axis 1 of themain spindle rotation motor 11. Thereby, the path R of the roughing tool2 calculated by shifting the path F of the finishing tool 3 by thefinishing allowance f in the direction perpendicular to the rotationcenter axis 1 of the main spindle rotation motor 11 is corrected so thata predetermined gap is formed between the workpiece W and the roughingtool 2, viewed in the direction of the rotation center axis 1 of themain spindle rotation motor 11. Thereby, the feed of the finishing tool3 (feed of the workpiece W) in the direction of the rotation center axis1 of the main spindle rotation motor 11 is not stopped, and the cut-ininto the inside of the finishing portion of the workpiece W by theroughing tool 2 can be prevented. As the result, the machining time ofthe workpiece W by the roughing tool 2 and the finishing tool 3 can bereduced. Further, because the feed of the finishing tool 3 (feed of theworkpiece W) is not stopped, the formation of the cutter mark on thesurface of the workpiece W by the finishing tool 3 can be suppressed.

[0076] Further, when the movement position of the roughing tool 2 iscorrected, because the movement position of the roughing tool 2 iscorrected so that the movement speed of the roughing tool 2 in thedirection perpendicular to the rotation center axis 1 of the mainspindle rotation motor 11 is a predetermined value, the path R of theroughing tool 2 is also corrected so that the movement speed of theroughing tool 2 in the direction perpendicular to the rotation centeraxis 1 of the main spindle rotation motor 11 is a predetermined value.Thereby, the roughing tool 2 can be smoothly moved, and the cutting loadof the workpiece W by the roughing tool 2 can be reduced, and thevariation of the cutting load can be suppressed.

[0077] Next, referring to FIG. 6 and FIGS. 7A and 7B, a varied exampleof the correction of the movement position (the path) of the roughingtool 2 will be described. The varied example shown in FIG. 6 and FIGS.7A and 7B is an example in which the movement position of the roughingtool 2 is corrected so that the roughing tool 2 moves at the equalacceleration.

[0078] The relative position of the finishing tool 3 to the workpiece W,at which the correction of the movement position of the roughing tool 2is to be started, is defined as follows. Initially, according to theformula (1), the time interval t to correct the movement position of theroughing tool 2 is found.

d/2=½×α×(t/2)²   (1)

[0079] d: The height of the stepped portion Wa of the workpiece W

[0080] α: The movement acceleration of the roughing tool 2

[0081] When the time interval t to correct the movement position of theroughing tool 2 is found, according to the formula (2), a divisiondistance L to correct the movement position of the roughing tool 2 isfound.

L=V _(Z) ×t  (2)

[0082] V_(Z): the feed speed of the workpiece W

[0083] Finally, according to the formula (3), the relative position(distance from the stepped portion Wa of the workpiece W) L₀ of thefinishing tool 3 to the workpiece W, at which the correction of themovement position of the roughing tool 2 is to be started, is found.

L ₀ =L+D  (3)

[0084] D: the offset amount between the roughing tool 2 and thefinishing tool 3

[0085] When the position of the finishing tool 3 in the direction of therotation center axis 1 of the main spindle rotation motor 11 reaches theposition apart by the difference L₀ from the stepped portion Wa of theworkpiece W, as shown in FIG. 6, the correction of the movement positionof the roughing tool 2 is carried out. That is, the movement position ofthe roughing tool 2 is corrected during a time period from the time whenthe roughing tool 2 reaches the position apart by the distance L fromthe stepped portion Wa of the workpiece W, to the time when theworkpiece W is fed by L/2. That is, the movement position of theroughing tool 2 is corrected in such a manner that, while the timeelapses by t/2 from the start of the correction of movement position ofthe roughing tool 2, as shown in FIGS. 7A and 7B, the roughing tool 2 isacceleratedly moved by the movement acceleration α, in the directionperpendicular to the rotation center axis 1 of the main spindle rotationmotor 11. Then, while the feed distance of the workpiece W from thestart of the correction of the movement position of the roughing tool 2is changed from L/2 to L, that is, the time from the start of thecorrection of movement position of the roughing tool 2 reaches from t/2to t, the movement position of the roughing tool 2 is corrected so thatthe roughing tool 2 is deceleratedly moved by the movementaccelerations, in the direction perpendicular to the rotation centeraxis 1 of the main spindle rotation motor 11.

[0086] As described above, when the correction of the movement positionof the roughing tool 2 is carried out from the time when the position ofthe finishing tool 3 reaches the position apart from the stepped portionWa of the workpiece W by the distance L₀ (the position of the roughingtool 2 apart from the stepped portion Wa of the workpiece W by thedistance L), the path R of the roughing tool 2 is prepared with apredetermined gap between the workpiece W and the roughing tool 2,viewed in the direction of the rotation center axis 1 of the mainspindle rotation motor 11. Therefore, the feed of the finishing tool 3in the direction of the rotation center axis 1 (the feed of theworkpiece W) is not stopped, and the cut-in into the inside of thefinishing portion of the workpiece W by the roughing too 12 can beprevented. As the result, the machining time of the workpiece W by theroughing tool 2 and the finishing tool 3 can be reduced. Further,because the feed of the finishing tool 3 (the feed of the workpiece W)is not stopped, the formation of the cutter mark on the surface of theworkpiece W by the finishing tool 3 can be suppressed.

[0087] Further, the movement position of the roughing tool 2 (the pathof the roughing tool 2) is easily corrected because the movementposition of the roughing tool 2 is corrected so that the roughing tool 2is moved while it is accelerated or decelerated at the movementacceleration a in the direction perpendicular to the rotation centeraxis 1 of the main spindle rotation motor 11. Further, because themovement speed of the roughing tool 2 after the start of the correctionand before the end of the correction is lower, the variation of thecutting load on the workpiece W by the roughing tool 2, vibration of thework piece W, and the vibration of the roughing tool 2, can be furthersuppressed, and the scar on the surface of the workpiece can be moresuppressed.

[0088] In this connection, in the present embodiment, it is structuredin such a manner that the workpiece can be moved in the direction of therotation center axis 1 of the main spindle rotation motor 11, and theworkpiece W is sent to this direction, but the present invention is notlimited to this, and it may be structured in such a manner that theroughing tool 2 and the finishing tool 3 are moved in the direction ofthe rotation center axis 1 of the main spindle rotation motor 11.

[0089] Further, in the present embodiment, it is structured in such amanner that the count section 53 is provided in the control unit section51, but, it may be structured in such a manner that the program is madeso that the central processing unit 52 performs the role of the countsection 53 utilizing the ROM 56 as storing means. Instead, a portion offunctions which are performed by the central processing unit 52 may bereplaced by the hardware circuit.

[0090] Further, in the present embodiment, it is structured in such amanner that the position data (movement position) of the roughing tool 2showing the path of the roughing tool 2 and the position data (movementposition) of the finishing tool 3 showing the path of the finishing tool3 are stored corresponding to every predetermined number of cumulativerotations of the main spindle rotation motor 11 (main spindle) andstored, and every time when the number of cumulative rotations of themain spindle rotation motor 11 (main spindle) reaches a predeterminedone, set in the position data table memory 57 a, the correspondingposition data of the roughing tool 2 and the finishing tool 3 areoutputted as the roughing tool position command signal and the finishingtool position command signal, but the present invention is not limitedto this. For example, it may be structured in such a manner that everytime when the number of cumulative rotations of the main spindlerotation motor 11 (main spindle) reaches a predetermined number ofcumulative rotations θ_(n), the position data (movement position) of theroughing tool 2 showing the path of the roughing tool 2 and the positiondata (movement position) of the finishing tool 3 showing the path of thefinishing tool 3 may be calculated and found, and outputted as theroughing tool position command signal and the finishing tool positioncommand signal.

[0091] As described above, the present invention provides a tool pathpreparing method and a machining method by which the machining time ofthe workpiece by the roughing tool and the finishing tool can bereduced, and the scar on the surface of the workpiece can be suppressed.

What is claimed is:
 1. A method of preparing a tool path tosimultaneously conduct a roughing and a finishing operations by movingat least one of a workpiece to be rotated around a predetermined axisand tools including a roughing tool and a finishing tool offset-arrangedin the axial direction of the predetermined axis, the method comprising:calculating a path of the roughing tool based on a path of the finishingtool by shifting the path of the finishing tool by a finishing allowancein the direction perpendicular to the predetermined axis; and correctingthe calculated path of the roughing tool so as to form a predeterminedgap between the workpiece and the roughing tool in the axial directionof the predetermined axis.
 2. The method according to claim 1, whereinthe path of the roughing tool is corrected so that the moving speed ofthe roughing tool in the direction perpendicular to the predeterminedaxis is a predetermined value.
 3. The method according to claim 1,wherein the path of the roughing tool is corrected so that the roughingtool moves at a predetermined acceleration from a position, at which thegap between the workpiece and the roughing tool in the axis direction ofthe predetermined axis becomes a predetermined value, in the directionperpendicular to the predetermined axis.
 4. A method of machining aworkpiece to be rotated around a predetermined axis, comprising:arranging tools including a roughing tool and a finishing tool offset inthe axial direction of the predetermined axis; calculating a path of theroughing tool based on a path of the finishing tool by shifting the pathof the finishing tool by a finishing allowance in the directionperpendicular to the predetermined axis; correcting the calculated pathof the roughing tool so as to form a predetermined gap between theworkpiece and the roughing tool in the axial direction of thepredetermined axis; and moving at least one of the workpiece and thetools, thereby simultaneously conducting a roughing and a finishingoperations.
 5. The method according to claim 4, wherein the path of theroughing tool is corrected so that the moving speed of the roughing toolin the direction perpendicular to the predetermined axis is apredetermined value.
 6. The method according to claim 4, wherein thepath of the roughing tool is corrected so that the roughing tool movesat a predetermined acceleration from a position, at which the gapbetween the workpiece and the roughing tool in the axis direction of thepredetermined axis becomes a predetermined value, in the directionperpendicular to the predetermined axis.
 7. A tool path preparing methodcomprising: reading initial positions of a roughing tool and a finishingtool; initializing the number of cumulative rotations of a workpiece tobe rotated around a predetermined axis; reading a position datacalculation program; settling a movement position of the finishing toolat a predetermined number of cumulative rotations of the workpiece;calculating a movement position of the roughing tool at thepredetermined number of cumulative rotations of the workpiece;correcting the calculated movement position of the roughing tool in adirection perpendicular to and away from the predetermined axis when agap between the roughing tool and the workpiece in the axial directionof the predetermined axis is not larger than a predetermined value; andstoring the movement position of the roughing tool and the finishingtool in a position data table memory.